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United States Patent |
5,638,039
|
Lehmann
,   et al.
|
June 10, 1997
|
Coil body made of synthetic material, an injection mold and method of
making the coil body
Abstract
A coil body with an upper section and at least one lower section which has
a downward cone shape. The coil body is manufactured from a thermosetting
plastic by an injection molding process such that the lower section is
provided along its full length with a thin molded tab. Furthermore, an
injection mold for forming of the coil body is provided. The lower section
of the mold is equipped with at least one blind cavity which is connected
to the mold cavity via a gap running the entire height of the mold cavity.
Inventors:
|
Lehmann; Eberhard (Pfedelbach-Windischenbach, DE);
Ahrens; Peter (Ohringen, DE)
|
Assignee:
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Hohenloher Spulenkoerperfabrik GmbH & Co. (Oehringen, DE)
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Appl. No.:
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311742 |
Filed:
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September 23, 1994 |
Foreign Application Priority Data
| Sep 23, 1993[DE] | 43 32 339.1 |
Current U.S. Class: |
335/198; 336/198 |
Intern'l Class: |
H01H 001/00 |
Field of Search: |
335/198,186
336/198,208,192
|
References Cited
U.S. Patent Documents
4135297 | Jan., 1979 | Guttenberger et al. | 29/629.
|
5420559 | May., 1995 | Ohshiba et al. | 336/208.
|
Other References
Von Werner Laeis, Koeln/Troisdorf, "Das Spritzgussverfahren in der
Revision*", Kunststoffe, (1961), pp. 97-103.
|
Primary Examiner: Donovan; Lincoln
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. A coil body, comprising:
an upper section and at least one lower section having a cone shape
projecting downwardly from the upper section;
wherein the upper section and the at least one lower section are
manufactured by an injection process such that the transition from upper
section to lower section is defined by a mold seam formed by a parting
line of an injection mold; and
wherein the at least one lower section includes a flange provided with a
thin tab, molded along a full height of the flange.
2. A coil body according to claim 1, wherein the tab is removable from the
flange.
3. A coil body according to claim 1, wherein the tab is connected to the
flange by a projection running parallel to the tab; and
wherein the projection is approximately equal to a dimensions of the
flange.
4. A coil body according to claim 1, wherein the at least one lower section
includes several lower sections.
5. A coil body according to claim 4, wherein the several lower sections
include four identically shaped flanges arranged symmetrically on the
upper section.
6. A coil body according to claim 1, wherein the upper section and lower
section include a thermosetting plastic.
7. A coil body according to claim 6, wherein the thermosetting plastic
includes an unsaturated polyester compound.
8. A coil body according to claim 1, wherein the tab has a thickness that
at a maximum is equal to one third of a diameter of the flange.
9. An injection mold, comprising:
an upper part and a lower part, each part having at least one mold cavity
for molding a coil body; and
a parting line joint formed between the cavities;
wherein at least one blind cavity in the lower part is connected to the
mold cavity therein via a gap running an entire height of the mold cavity.
10. An injection mold according to claim 9, wherein the blind cavity is
connected at an upper end to a venting core.
11. An injection mold according to claim 10, wherein a volume of the blind
cavity is at least as great as a volume of the mold cavity to which the
blind cavity is connected.
12. An injection mold according to claim 9, wherein the lower part includes
several evenly arranged mold cavities, each provided with a respective
blind cavity.
13. An injection mold according to claim 9, wherein a thickness of the gap
is narrower than a diameter of the mold cavity such that the gap forms a
thin tab on the coil body.
14. A coil body, comprising:
an upper section and at least one lower section having a downwardly shaped
cone;
wherein the upper section and the at least one lower section are
manufactured by an injection molding process such that a transition from
upper section to lower section is defined by a molded seam which has been
formed by joints of an injection mold; and
wherein the at least one lower section includes a flange provided along the
full height of the flange with a molded breaking edge.
15. A method of manufacturing an injection molded coil body having an upper
and a lower section, comprising the steps of:
injecting synthetic material in plastic form under high pressure into an
injection mold;
providing essentially in a mold release direction of the mold at least one
mold cavity sealed by a melt front of the material;
forming a thin tab on said lower section by molding along the height of the
mold cavity parallel to the mold release direction; and
providing the mold cavity with a volume that is connected to a compensating
volume.
16. The method according to claim 15, wherein the step of providing the
mold cavity with a volume further comprises the step of providing a blind
cavity for the compensating volume.
17. The method according to claim 15, further comprising the step of
pushing, by the melt front of the synthetic material, air present in the
injection mold into a venting core connected to the compensating volume.
Description
BACKGROUND OF THE INVENTION
The invention relates to a coil body made of synthetic material, wherein
the coil body is provided with an upper and lower section each made from
an injection process. The invention further relates to an injection mold
for making the coil body and the method for manufacturing the coil body.
DESCRIPTION OF THE RELATED ART
There are various known embodiments of coil bodies used as electrical
components, which are inserted by their contact pins into predrilled holes
in a printed circuit board.
These coil bodies consist of a single component that typically has a number
of flanges on the bottom. These flanges are used as spacers between the
coil body and the printed circuit board. These flanges form the lower
section of the coil body. Generally, coil bodies are manufactured by an
injection molding process using a thermoplastic. During this process the
upper section of the coil body is formed in an upper part of an injection
mold and the flanges in a lower part of an injection mold. As a result,
coil bodies manufactured in this manner show a visible mold seam caused by
the parting line of the injection mold.
The miniaturization of electronic components means that the size of coil
bodies used must constantly decrease. The simultaneously increasing
performance of components leads to greater warming of the coils. For that
reason, insulating varnish with an ever higher melting point must be used
for the wires of the coil windings.
In order to solder the ends of the windings to the contact pins molded into
the coil body, the soldering temperature must be higher than the melting
temperature of the insulating varnish. However, when the soldering
temperature is greater than the melting temperature of the thermoplastic,
the coil body softens during soldering. Thus, the contact pins may become
loose and the component fails later on during use.
To avoid this problem, the insulating varnish must currently be removed
manually from the ends of the windings. This allows the soldering to be
performed at a temperature that is below the melting temperature of the
coil body material.
A remedy for this problem is the use of a thermosetting plastic instead of
a thermoplastic. However, a problem occurs because the injection molds
used for this type of coil body cannot work with thermosetting plastics,
because of the different setting behaviors of thermoplastics and
thermosetting plastics. Normally, a thermoplastic solidifies during
cooling. In thermosetting plastic, the solidification takes place during
the curing process when a crosslinking of the molecular structures occurs.
FIGS. 7 to 9 illustrate how a coil body is presently manufactured. The
injection mold consists of an upper mold 1 and a lower mold 2. Mold cavity
4 for the upper section of the coil body is provided in the upper part of
the injection mold and mold cavities 3 for forming flanges are located in
the lower part of the mold 2. As shown in FIG. 9, the injected plastic 9
flows from the upper part 1 of the mold into cavities 3 of injection mold
lower part 2. Because of the relatively long period of time the
thermoplastic remains in a liquid phase, the air displaced from the mold
cavities is able to escape through the material via a venting core 80
along the parting line of the mold sections. But as discussed above the
coil body of this material is likely to melt during the soldering process.
Alternatively, if a thermosetting plastic, in which the curing starts very
quickly, is injected into this mold, when the melt front has passed the
venting core 80, this core is sealed a short time later by the already
hardened thermosetting plastic. This results in an air pocket 20 being
formed in mold cavity 3. The air in the air pocket 20, although
compressed, is unable to escape via the venting core. The result of this
is that the flanges are not fully formed. More particularly, the flanges
are not of the same structure.
SUMMARY OF THE INVENTION
One of the objectives of the invention is to provide an improved coil body
manufactured from thermosetting plastic.
Another objective of the invention is to develop an injection mold that can
be used to manufacture these coil bodies.
An alternative objective of the invention is to develop a suitable
injection molding process used for making the coil bodies.
To achieve the objective of the coil body of the present invention, a coil
body with an upper section and at least one lower section having a
downward cone shape is provided. The coil body is manufactured by an
injection molding process such that the transition from upper section to
lower section is defined by a mold seam, which has been formed by the
parting line of the injection mold. The lower section is provided with a
flange having a thin tab molded along its full height. Because the lower
section of the coil body is provided with a thin tab over its full height,
compared to the diameter of the lower section, there is a space created
independent of the working cavities through which the air displaced by the
melt front escapes.
When a projection which is dimensioned similar to the lower section is cast
on the other end of the tab, the escape of all the compressed air volume
of the lower section is ensured by it escaping into the projection. This
projection has no function as far as the coil body is concerned. It may be
removed together with the molded breaking edge tab following forming, so
that it does not matter whether casting defects appear in it. When the
thickness of the tab is a maximum of one third of the diameter of the
lower section, the removal of the projection is simplified.
The objective of developing an injection mold for manufacturing the coil is
achieved by providing an injection mold with an upper part and a lower
part, in which the mold cavities for molding a coil body are formed
between a mold seam. At least one blind cavity in the lower die part is
connected to the mold cavity via a gap running the entire height of the
mold cavity intended for the coil body.
The blind cavity is provided in the lower part of the injection mold to
form a tab on the lower section at the coil body. The blind cavity is
connected to the mold cavity via a gap running the entire height of the
mold cavity. This ensures that the melt front changes from the vertical
flowing direction of the prior art to a horizontal direction. When the
blind cavity is connected with its upper end to a horizontal venting core,
the complete release of the air in the cavity is ensured.
This injection mold helps achieve the objective of providing a method of
manufacturing a coil body with an upper and a lower section. During the
method, synthetic material in plastic form is injected under high pressure
into an injection mold, which has essentially in the mold release
direction, at least one mold cavity sealed by the melt front of the
material. This process allows a thin tab to be molded along the height of
the mold cavity parallel to the mold release direction. The mold cavity
volume is connected to a compensating volume.
This process provides a directional change of the melt front, from the
prior art of FIGS. 7-9, at the end of the molding process. This ensures
that the component parts of the coil body are fully formed and that no air
is trapped in the mold cavities by the poured in synthetic material
because the air can be pushed out of the injection mold through the
venting core running parallel to the melt front.
In order to ensure that the forming in the mold cavity is completed, the
volume of the blind cavity preferably corresponds to the volume of the
mold cavity. When a coil body with several lower sections, for example
flanges, is to be molded, then each of the mold cavities should be
provided with its own blind cavity.
A coil body, injection mold, and method of manufacture of the coil body
according to the invention provide the objectives as stated above, which
will become apparent from the detailed description given hereafter. It
should be understood, however, that the detailed description, while
indicating a preferred embodiment of the invention, is given by way of
illustration only since various changes and modifications within the scope
of the invention will become apparent to those skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of the specification, illustrate a presently preferred embodiment of the
invention, and, together with the general description given above and the
detailed description of the preferred embodiment given below, serve to
explain the principles of the invention.
FIG. 1 shows a partial section through the injection mold of the present
invention;
FIG. 2 shows a partial top view of the lower part of the injection mold
along line II--II shown in FIG. 1;
FIG. 2a shows a top view of the lower part of a plurality of injection
molds of the present invention;
FIGS. 3-5 show the progression of the melt front of the injected synthetic
material, as it proceeds through the injection mold of FIG. 1;
FIG. 6 shows the coil body of the present invention;
FIG. 6a shows a bottom view of the coil body shown in FIG. 6;
FIG. 7 shows a partial section through an injection mold of current
technology;
FIG. 8 shows a partial top view of the lower part of the mold along line
VIII--VIII as shown in FIG. 7;
FIG. 9 shows a representation of the flow of a thermosetting plastic in the
injection mold according to FIG. 7 at the end of the molding process.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The coil body 10 of the present invention is shown in FIG. 6. The coil body
10 consists of an upper section 14 with attached, downwardly projecting
flanges 13. As shown in FIG. 6a, the coil body 10 has four symmetrically
arranged flanges 13 on upper section 14. Several contact pins 11, which
are soldered to the coil windings, are set into the lower section of the
coil body 10. The flanges 13 serve as spacers for the coil body 10 on a
printed circuit board, not illustrated here, in which the contact pins 11
are inserted.
The upper section 14 of the coil body 10 is formed in the upper part of the
injection mold 1 and the flanges 13 are formed in the lower part of the
injection mold 2. As a result, the parting line joint 5 of the mold
sections leaves a mold seam 15 on coil body 10. This mold seam 15 forms
the division between the coil body upper section 14 and flanges 13 which
comprise the lower section of the coil body. Along the entire length H of
the flanges 13, a thin tab 12 is molded. The thickness of the tab 12
decreases downward in a cone-shaped fashion compared to the diameter of
flanges 13.
Illustrated in FIGS. 1-5 is the injection mold according to the present
invention. For convenience, the same reference numerals have been used for
those components of the injection mold of the current technology shown in
FIGS. 7 and 8.
The injection mold of the present invention consists of an upper part of
the mold 1 and a lower part 2 which can be joined together, in a known
fashion, such that the molded components can be formed with a mold seam 15
created between them. Mold cavity 4, located in upper part of the mold 1,
is used for forming the upper section of the coil body 14. Mold cavity 3,
in the lower part of the mold 2, is used to form the flanges 13. Mold
cavity 3 is cone-shaped in a downward direction from cavity 4 and its
upper area 3' is greater in diameter than the lower area 3".
As shown in FIGS. 1 and 2, at the side of the mold cavity 3 and extending
across the entire height I, a downward progressing vertical gap 6 is
provided in the lower part of the mold 2. This vertical gap 6 opens at one
end to the mold cavity 3 and at its other end to a blind cavity 7. The
blind cavity 7 is also a mold cavity having a volume that is at least
equal to the volume of mold cavity 3. The blind cavity 7 is called thus
because it produces a component that is not necessary for the molded coil
body 10. The blind cavity 7 at its upper end 7' is connected to a venting
core 8. Both gap 6 and blind cavity 7 are cone shaped, which is necessary
for the removal of the molded component. FIG. 2a is a top view of the
lower part of the mold 2 showing several evenly spaced mold cavities 3,
each provided with a blind cavity 7.
As shown in FIGS. 3-5, the injected thermosetting plastic 9, which
preferably is an unsaturated polyester compound, flows through mold cavity
4 into mold cavity 3. The air thereby expelled escapes into the narrow gap
6. Mold cavity 3 and gap 6 are filled evenly with plastic, while the melt
front moves on in the direction of the blind cavity 7. Because the flow of
the material in the present invention is not in the vertical direction as
with the prior art, but in a horizontal direction (see FIG. 5), the air is
fully evacuated from blind cavity 7 via venting core 8.
After the molded component has cured, it is removed from the mold in the
known manner, not illustrated here, using an ejection ram.
It will be understood that various modifications in the form of the
invention as described herein in its preferred embodiment may be made
without departing from the spirit thereof and of the scope of the claims
which follow.
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